THIS INVENTION relates to copolymerization. It relates in particular to a copolymer of propylene and 1-pentene, to a process for producing such a copolymer, and to a polymer composition which includes such a copolymer.
According to a first aspect of the invention, there is provided, broadly, a copolymer of propylene and 1-pentene.
The copolymer may, more particularly, have a random arrangement of propylene and 1-pentene, ie it may be a random copolymer of propylene and 1-pentene. The copolymer may be thermoplastic, and may have crystalline and amorphous sequences.
The copolymer may further be characterized by the substantial absence of monomer sequences other than propylene and 1-pentene.
About 0.05% to 20% by mass of the copolymer may be derived from 1-pentene, with the balance thus being derived from propylene.
The melt flow index of the copolymer may be in the range of about 0.01 to about 200 g/10 minutes, preferably in the range 0.5 to about 60 g/10 minutes.
The copolymer may comply with the formula
IS greater than 0.5Y+5
where IS is the impact strength thereof, expressed in Kj/m2, and Y is the weight percent of 1-pentene in the copolymer. The copolymer may also have a haze value lower than 7.5% when measured according to ASTM 1003-92, on a film of 100 xcexcm.
The copolymer may be that obtained by reacting propylene and 1-pentene in a reaction zone, while maintaining a pressure between 1 and 60 kg/cm2 in the zone, at a reaction temperature between 0xc2x0 C. and 100xc2x0 C., and for a reaction time between 20 minutes and 8 hours, in the presence of a suitable Ziegler-Natta catalyst or catalyst system. Still more particularly, the copolymer may be that obtained by continuously varying, during the reaction of the propylene and the 1-pentene, the ratio of the concentration of the propylene to that of the 1-pentene.
Thus, according to a second aspect of the invention, there is provided a process for producing a copolymer, which process comprises reacting propylene and 1-pentene in a reaction zone, while maintaining a pressure between 1 and 60 kg/cm2 in the zone, at a reaction temperature between 0xc2x0 C. and 100xc2x0 C., and for a reaction time between 20 minutes and 8 hours, in the presence of a suitable Ziegler-Natta catalyst or catalyst system.
The process may include continuously varying the ratio of the concentration of the propylene to that of the 1-pentene in the reaction zone, so that the copolymer has a random arrangement of propylene and 1-pentene. In other words, the copolymer is then a random copolymer of propylene and 1-pentene, which can also be referred to as xe2x80x98n-pentene-1xe2x80x99.
While the reaction temperature can be in the range of 0xc2x0 C. to 100xc2x0 C. as stated hereinbefore, it is preferably in the range of 20xc2x0 C.-80xc2x0 C., still more preferably in the range 40xc2x0 C.-70xc2x0 C.
Since propylene is a gas at atmospheric pressure, the reaction zone is thus provided by a closed reaction vessel, with the zone pressure being in said range of 1-60 kg/cm2. Preferably, the pressure is in the range 3-30 kg/cm2, more preferably in the range 6-14 kg/cm2.
The reaction will thus be continued for a sufficient period of time to obtain a desired degree of conversion of the monomers. Typically, the conversion can be in the range 10%-95%. Thus, the reaction time will normally be between said 20 minutes and 8 hours, preferably between 40 minutes and 2 hours.
The reaction is preferably carried out in a single reaction zone, ie a single stage reactor vessel is preferably used. The reaction can be effected in a batch fashion, with all the monomers, ie the propylene and 1-pentene, being added simultaneously at the start of the reaction to the reaction zone, and no product being removed therefrom during the course of the reaction. Thus, the continuous variation in the ratio of the concentration of the propylene to that of the 1-pentene during the reaction is achieved by virtue of the monomers being consumed at unequal rates during the reaction, ie the monomers have different reaction rates. Instead, the process may be a semi-continuous process, wherein at least one of the monomers is added continuously to the reaction zone over a period of time with the other monomer then either also being added continuously over the period of time or being added at the start of the reaction, and with no products being removed. The continuous variation in the relative concentrations of the monomers is then achieved through the unequal rates of consumption of the monomers during the reaction, as well as rates of addition of the monomers. In yet a further embodiment, the process may be a continuous process, involving the continuous addition of the monomers to the reaction zone, and the continuous removal of products therefrom. In such case, the continuous variation in the relative concentrations of the monomers is effected by means of the unequal rates of consumption thereof, as well as by the addition rates of the monomers and the withdrawal rate of product from the reaction zone.
The reaction is preferably also carried out in slurry phase. Accordingly, the monomers and/or the catalyst may be suspended in a suitable inert slurrying agent. The slurrying agent may be a saturated, aliphatic or cyclo-aliphatic liquid hydrocarbon. In particular the hydrocarbon may have from 2-12 carbon atoms. Most preferred are aliphatic hydrocarbons having 6 and 7 carbon atoms. The volume or proportion of slurrying agent used is not critical, but should be sufficient to permit good agitation of the resultant slurry, and efficient heat transfer. Thus, sufficient slurrying agent may be used to achieve a slurry concentration in the range of 4 g-400 g of polymer per liter of slurrying agent, preferably 50-250 g/l.
The molecular weight of the resultant random copolymer can be regulated by adding hydrogen to the reaction zone. The greater the amount of hydrogen added, the lower will be the molecular weight of the random copolymer. A hydrogen partial pressure of 0.1-2 kg/cm2 is suitable for a reaction zone pressure of 3-30 kg/cm2.
Any Ziegler-Natta catalyst or catalyst system, suitable for propylene polymerization, can, at least in principle, be used. Thus, a catalyst system comprising a titanium-based Ziegler-Natta catalyst and, as a co-catalyst, an organo-aluminium compound, and wherein the atomic ratio of aluminium to titanium in the catalyst system is between 0.1:1 and 100:1, preferably 0.65:1 and 65:1, may be used.
Sufficient of the titanium-based Ziegler-Natta catalyst should then be used such that the concentration of titanium is at least 0.0001 mole %, based on the total monomer addition to the reaction zone. Preferably, the concentration thereof should be in the range 0.0003-0.15 mole % titanium.
Typical titanium components of the Ziegler-Natta catalyst are titanium trichlorides of xcex1, xcex2, xcex3 and xcex4 type, and titanium trichlorides or titanium tetrachloride carried on a support. Catalyst support and activation can be effected in known fashion. For the preparation of a titanium catalyst, halides or alcoholates of trivalent or tetravalent titanium are normally used. TiCl4 is especially preferred.
In addition to the trivalent and tetravalent titanium compounds and the support or carrier, the catalyst can also contain electron-donor compounds, e.g. mono or poly functional carboxyl acids, carboxyl anhydrides and esters, ketones, ethers, alcohols, lactones, or phosphorous or silicon organic compounds. Electron-donor compounds improve activity, stereoregularity and granulometric properties of the catalyst.
A preferred titanium-based catalyst is (TiCl3)3 AlCl3 commercially available with a content of 76.5-78.5 TiCl3 weight percent. Another preferred titanium catalyst is xcex4-TiCl3 (AlCl3)⅓ (n-propyl benzoate), which is commercially available.
Typical organo aluminium compounds which can be used in combination with the titanium-based catalyst are compounds expressed by the formula Al Rm X3-m wherein R is hydrogen or a hydrocarbon residue of 1-15 carbon atoms, X is a halogen atom or an alkoxy group of 1-15 carbon atoms, and m is a number represented by 0 less than m less than 3. Specific examples of suitable organo aluminium compounds which can be used are: a trialkyl aluminium, a trialkenyl aluminium, a partially alkoxylated alkyl aluminium, an alkyl aluminium sesquialcoxide, a partially halogenated alkyl aluminium, an alkyl aluminium sesquihalide, an alkyl aluminium dihalide, a partially hydrogenated alkyl alumina, an alkyl aluminium dihydride, and an alkyl aluminium oxyhalide. The most preferred organo aluminium compound is diethylaluminium chloride. Triethyl aluminium is the most preferred compound when working with magnesium chloride supported titanium catalyst in the presence of an electron donor.
The copolymer obtained from the process shows a random monomer distribution controlled by the ratio of the monomers used, and the reaction conditions. Thus, in the copolymer, the portion attributed to propylene can be in the range of 80-99.95% by weight, based on the weight of the copolymer, preferably in the range of 94%-99%. In other words, the portion attributed to 1-pentene can be in the range of 0.05%-20% by weight, preferably in the range of 1-6% by weight, as stated hereinbefore.
The Applicant is aware that polypropylene copolymers are sensitive to oxidation and normally are not used without adequate stabilization. The copolymers according to this invention can thus be stabilized in the same fashion as for the propylene copolymer stabilization.
An improved stabilization system for stabilization of copolymers according to the invention, thereby decreasing their termooxidative degradation and improving their long term heat stability is, however, also provided.
Thus, according to a third aspect of the invention, there is provided a polymer composition, which comprises
as component (i), a copolymer of propylene and 1-pentene;
as component (ii), at least one phenolic stabilizer; and
as component (iii), at least one organic phosphite stabilizer; and/or
as component (iv), at least one thioether stabilizer; and/or
as component (v), at least one metal salt of a higher aliphatic acid, with the proviso that at least one of components (iii), (iv) and (v) is present.
The copolymer of propylene and 1-pentene may thus be as hereinbefore described.
Component (ii) may comprise an organic phenolic stabilizer having a molecular mass exceeding 300 and/or a monomeric phenolic stabilizer.
A large range of known phenolic compounds can be used as the organic phenolic stabilizer or antioxidant. These include alkylphenols, hydroxyphenylpropionates, hydroxybenzyl compounds, and alkylidene bisphenols. As mentioned, the preferred phenolic stabilizers are those with molecular mass greater than 300. The most preferred phenolic stabilizers are those with a molecular mass greater than 600. Examples of preferred stabilizers are
tetrakis methylene(3,5-di-t-butyl-4-hydroxyhydrocinnamate)methane
octadecyl-3-(3,5-di-t-butyl-4-hydroxyphenyl)propionate
1,3,5-tris(3xe2x80x2,5xe2x80x2-di-t-butyl-4xe2x80x2hydroxybenzyl)-s-triazine-2,4,6-(1H,3H,5H)trione
2,2xe2x80x2thiodiethyl-bis-(3,5-di-t-butyl-4-hydroxyphenyl)propionate
A monomeric phenolic stabilizer is a dual functional compound having an antioxidant function and also being capable of polymerization, ie having a polymerizable group. It can be incorporated in the copolymer by a physical method, e.g. by melt mixing it with the copolymer or by mixing the copolymer with the homopolymer of the monomeric phenolic stabilizer or antioxidant. It can, however, also be incorporated in the copolymer by copolymerization. The preferred method of incorporation of the monomeric phenolic stabilizer is by graft copolymerization with the copolymer, initiated by radical initiators and/or by mechanical shearing in a molten state. The preferred radical initiators are peroxides. Examples of classes of peroxides which can be used are diacyl peroxides, dialkyl peroxidicarbonates, peresters, alkyl hydroperoxides, and dialkyl peroxides. The most preferred peroxide is the dicumyl peroxide.
More particularly, the monomeric phenolic stabilizer has, in addition to the polymerizable group, a hindered phenolic group providing the antioxidant function. Preferred monomeric phenolic stabilizers are those having a 3,5-bis(1,1-dimethylethyl)-4-hydroxyphenyl group providing the antioxidant function, attached to a vinyl polymerizable group. Examples of such monomeric phenolic stabilizers are
2,6-bis(1,1-dimethylethyl)-4-(1-methylethenyl)phenol
2,6-bis(1,1-dimethylethyl)-4-(4-pentenyl)phenol
2,6-bis(1,1-dimethylethyl)-4-(3,3-dimethyl-1-butenyl)phenol
2,6-bis(1,1,-dimethylethyl)-4-(2-propenyl)phenol
The most preferred monomeric phenolic stabilizer is 2,6-bis(1,1-dimethylethyl)-4-(ethenyl)-phenol.
A monomeric phenolic stabilizer grafted onto the copolymer chain inhibits the loss of the antioxidant during processing through volatility, migration or extraction with solvents. The use of a mixture of an organic phenolic stabilizer and a monomeric phenolic stabilizer grafted onto the copolymer is an exceptional combination which brings about particularly beneficial short and long term stabilization effects.
The composition can thus additionally include component (iii). While, at least in principle, any organic phosphite stabilizer can be used, it preferably has a molecular mass in excess of 300. Examples of such organic phosphite stabilizers are:
tris(2,4-di-t-butylphenyl)phosphite
tris(4-nonylphenyl)phosphite
tetrakis(2,4-di-t-butylphenyl)-4,4xe2x80x2-diphenylenebis-phosphonite
bis(2,4-di-t-butylphenyl)pentaerythritoldiphosphite
The use of an organic phosphite stabilizer together with a phenolic antioxidant and especially with a mixture of an organic phenolic antioxidant and a monomeric phenolic antioxidant grafted onto the copolymer chain increases the stability of the propylene/1-pentene copolymer to thermooxidative degradation, and provides particularly good long term heat stability.
The composition may instead, or additionally, include component (iv). The thioether stabilizer of component (iv) may be selected from the group consisting in dilauryl thiodipropionate, distearyl thiodipropionate, dimyristyl thiodipropionate, and dioctadecyl disulphide.
The presence of such a thioether stabilizer increases the stabilization properties of the phenolic stabilizer or antioxidant. The use of a thioether stabilizer with a mixture of an organic phenolic antioxidant and a monomeric phenolic antioxidant grafted onto the copolymer chain confers excellent degradation stability to the propylene/1-pentene copolymer.
The composition may instead, or additionally, include component (v). The metal salt of component (v) may be an alkaline earth metal salt, such as a magnesium salt, a calcium salt, or a barium salt; an alkali metal salt; a zinc salt; a cadmium salt; or a lead salt of a higher aliphatic acid such as stearic acid, lauric acid, capric acid or palmitic acid. The most preferred metal salt is calcium stearate.
When a higher aliphatic acid metal salt is added to a propylene-1-pentene copolymer or a propylene/1-pentene copolymer composition according to this invention, the metal salt is capable of sufficiently absorbing residual chloride originating from the catalyst used to produce the copolymer.
In one embodiment of the invention, the polymer composition may comprise
In another embodiment of the invention, the polymer composition may comprise
In yet another embodiment of the invention, the polymer composition may comprise
In these embodiments, the ratio of the organic phenolic stabilizer to the monomeric phenolic stabilizer can be varied over the entire range possible, ie from 100% of organic phenolic stabilizer and no monomeric phenolic stabilizer to 100% of monomeric phenolic stabilizer and no organic phenolic stabilizer.
Additionally, the composition may include other antioxidants, light stabilizers, antistatic agents, antiblocking agents, slip agents, nucleating agents, inorganic and organic fillers, inorganic and organic pigments, blended with the propylene/1-pentene copolymers.